The present invention relates to a control apparatus for a hybrid vehicle in which a propulsion force for running the vehicle is generated by output from an engine assisted by an electric motor as required.
Heretofore, there is known a hybrid vehicle incorporating an electric motor in addition to an engine as a drive source for vehicle propulsion.
One type of such hybrid vehicle is a parallel hybrid vehicle wherein an electric motor rotated by electricity is used as an auxiliary drive source for assisting the output from an engine, being an internal combustion engine. In this parallel hybrid vehicle, various control is carried out, such as assisting the output from the engine by means of the electric motor at the time of acceleration for example, and charging a battery by deceleration regeneration at the time of deceleration, so that the stored charge of the battery can be maintained while satisfying the requirements of the driver. (For example, as disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 7-123509.)
An engine, being an internal combustion engine, sometimes generates unpleasant vibrations at the time of low speed, that is, when idling. In a hybrid vehicle as described above, an electric motor that can reliably control torque electrically is incorporated into the engine, so that the engine vibration can be suppressed by controlling the torque of this electric motor. The present inventor has filed a first application for an engine vibration damping apparatus using such an electric motor (Japanese Unexamined Patent Application, First Publication No. Hei 9-248374).
Such an engine vibration control apparatus generates a plurality of different sine waves in proportion to the rotational frequency of the engine output shaft depending on the running conditions of the engine, generates a composite wave of these sine waves as a torque waveform for the electric motor to generate to reduce the torque variation of the engine output shaft, and controls the vibration by controlling the electric motor according to this composite wave torque waveform. In order to operate such an engine vibration damping apparatus, some energy may be consumed.
Accordingly, if such vibration damping control is performed at the time of idling for example, depending on the state of power being consumed elsewhere in a vehicle, such as lighting, wiper operation, or furthermore the operation of a car stereo or the like, the electric power supply generated by the engine may be insufficient, and the deficiency is drawn from the electric motor battery, resulting in the stored charge of the electric motor battery being reduced. In this manner, if the stored charge of the electric motor battery is reduced, assistance cannot be given to the engine even if the conditions require it.
The present invention takes into consideration the above situation, with an object of providing a control apparatus for a hybrid vehicle that prevents a situation in which a stored charge of an electric motor battery is reduced below a minimum required due to the vibration damping control device being operated, in other words, priority is given to preventing the stored charge of the electric motor battery being reduced below the minimum required, so that the occurrence of a situation that requires assistance to the engine by the electric motor can be handled without fail.
Furthermore, the present invention has an object of providing a control apparatus for a hybrid vehicle that can prevent the stored charge of the electric motor battery from being reduced below the minimum required at the time of idling, and additionally can increase the stored charge.
To achieve the abovementioned objects, a control apparatus for a hybrid vehicle (for example, an ECU in embodiments) of a first aspect of the invention comprises: an engine (for example, an engine 11 in the embodiment) which outputs a propulsion force for a vehicle; an electric motor (for example, a motor 12 in the embodiment) which assists the output from the engine; a battery (for example, an electric motor battery 17 in the embodiment) for an electric motor that drives the electric motor and also stores electric power generated by the electric motor; and a storage state monitoring device (for example, a current sensor 24 and an ECU 15 in the embodiment) which monitors the stored charge of the electric motor battery, and is characterized in that one condition for permitting operation of vibration damping control by the electric motor, for suppressing vibration caused by torque variation of the engine, is that a stored charge of the electric motor battery detected by the battery storage state monitoring device must be greater than a predetermined stored charge threshold, and when the condition is satisfied, vibration damping is performed by the vibration damping device, or alternatively when the condition is not satisfied, vibration damping by the vibration damping device is inhibited.
Here, vibration damping control for controlling engine vibration by the electric motor is performed through a vibration damping device (for example, a power drive unit 16 in the embodiment).
With such a construction, only in the case where the stored charge of the electric motor battery is greater than a predetermined stored charge threshold, that is, only in the case where there is some surplus stored charge in the electric motor battery, is vibration damping control performed by the vibration damping device. Accordingly, a situation does not occur in which there is no surplus stored charge of the electric motor battery, leading to the stored charge of the electric motor battery being reduced below the minimum required due to the operation of the vibration damping control device.
A second aspect of the invention is characterized in that conditions for permitting operation of vibration damping control require that, in addition to a stored charge of the electric motor battery detected by the storage state monitoring device being greater than a predetermined stored charge threshold (for example, a determination of step S9 in the embodiment), the vehicle is idling (for example, a determination of step S1 of the embodiment), engine speed is within a prescribed range (for example, a determination of step S5 in the embodiment), and engine load is within a prescribed range (for example, a determination of step S6 in the embodiment), and vibration damping control is performed when all conditions are satisfied.
With such a construction, it is possible to perform vibration damping control in a state where there is some surplus stored charge in the electric motor battery, the vehicle is idling, and the engine rotation is stable in regard to the engine speed and engine load, but excepting a case where a high load is required on the engine, that is, only when vibration damping control is genuinely required.
A third aspect of the invention is characterized in that conditions for permitting operation of the vibration damping device require that an electrical load of the vehicle excluding the electric motor is greater than a predetermined electrical load threshold (for example, a determination of step S10 in the embodiment), and when the electrical load exceeds the predetermined electrical load threshold, vibration damping control by the vibration damping device is performed for a predetermined limited time (for example, step S12 in the embodiment), and conversely, when the electrical load is less than or equal to the predetermined electrical load threshold, vibration damping control by the vibration damping device is performed without any set time limit (for example, step S11 in the embodiment).
With such a construction, in the case where the electrical load of the vehicle is high, the electric power produced by the engine is insufficient, and the deficiency is drawn from the electric motor battery, vibration damping control can be performed only for a predetermined limited time. Accordingly, it is possible to prevent a situation in which the amount of electric power drawn from the electric motor battery is increased and the stored charge of the electric motor battery reduced, due to performing vibration damping control over a long time.
A fourth aspect of the invention is characterized in that when the electrical load exceeds a predetermined electrical load threshold, and vibration damping control by the vibration damping device is performed for a predetermined limited time, engine speed is increased as an elapsed time of vibration damping control increases (for example, steps S13, S15 and S17 in the embodiment).
With such a construction, when the engine speed increases, the amount of generation by the engine increases, and the amount of electric power drawn from the electric motor battery decreases. Consequently, it is possible to minimize the decrease of the stored charge of the electric motor battery. Furthermore, when the engine speed increases, the vibration that occupants experience is reduced.
A fifth aspect of the invention is characterized in that when increasing engine speed, this is increased in stages as the elapsed time of vibration damping control increases (for example, steps S13, S15 and S17).
With such a construction, in the case where vibration damping control is discontinued after a predetermined time has passed, since the engine speed is increased in stages, and vibration damping control is discontinued in a state of lower sensation of vibration, occupants experience little unpleasant sensation caused by engine vibration.
Incidentally, if vibration damping control is discontinued when the engine speed is low, the difference in vibration felt physically between when vibration damping control is performed and when not performed is considerable, so that the unpleasant sensation experienced by occupants increases when vibration damping control is discontinued.
A sixth aspect of the invention is characterized in that when the engine is idling (for example, a determination of step SA1 in the embodiment), when the stored charge detected by the storage state monitoring device is greater (for example, a determination of step SA8 in the embodiment) than a predetermined stored charge threshold (for example, a first threshold value in the embodiment), vibration damping control for controlling the vibration damping of the engine is performed by the electric motor (for example, processing of step SA14 in the embodiment), and conversely, when the stored charge of the battery is less than or equal to the stored charge threshold value (for example, a determination of step SA8 in the embodiment), vibration damping control by the electric motor is inhibited (for example, processing of step SA10 in the embodiment), and when the stored charge of the battery detected by the storage state monitoring device is less than a predetermined second threshold that is lower than the stored charge threshold value (for example, determination of steps SB7 and SC7 in the embodiment), the idling speed of the engine is increased (for example, processing of steps SB10 and SC11 in the embodiment).
In this manner, when the stored charge of the battery detected by the storage state monitoring device is less than or equal to the predetermined stored charge threshold, vibration damping control by the electric motor is stopped, and thus first of all power consumption is suppressed. However, the stored charge of the battery still decreases, and when the stored charge of the battery detected by the storage state monitoring device is less than the predetermined second threshold that is lower than the stored charge threshold, the idling speed of the engine is increased, and the drive torque of the engine is increased. As a result, it is possible to increase the torque that can be distributed as generation torque for the electric motor to generate electricity, enabling an increase in the amount of charge to the battery.
In a seventh aspect of the invention, when the stored charge of the battery detected by the storage state monitoring device is the same as the second threshold or less than a third threshold that is even lower (for example, determinations of steps SB7 and SC7 in the embodiment), if the arrangement is such that mechanical loads, other than the drive torque of the electric motor driven by the engine, are removed from the drive torque (for example, processing of steps SB9 and SC10 in the embodiment), it is possible to further increase the torque that can be distributed as generation torque for the electric motor to generate electricity.
In an eighth aspect of the invention, if a mechanical load is either drive torque of an air conditioner compressor (for example, a compressor 27 in the embodiment) or creeping torque (for example, steps SB9 and SC10 in the embodiment), since these torques are large it is possible to effectively increase the torque that can be distributed as generation torque for the electric motor to generate electricity.